Enhanced inactivation of Escherichia coli and Listeria monocytogenes by exposure to 405 nm light under sub-lethal temperature, salt and acid stress conditions

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Abstract

The antimicrobial effects of 405 nm light have generated interest in its use as an emerging disinfection technology with potential food-related applications. The aim of this study was to assess the bactericidal efficacy of 405 nm light for inactivation of Escherichia coli and Listeria monocytogenes under sub-lethally stressed environmental conditions. Bacteria were exposed to 405 nm light from a light emitting diode (LED) array under various temperature, salt (NaCl) and acid conditions to determine if bacterial susceptibility to 405 nm light inactivation is affected when exposed under these conditions. Non-stressed bacterial populations (105 CFU/mL) were exposed to increasing doses of 405 nm light (~ 70 mW/cm2) and the inactivation results were compared with those generated under stress conditions. Bacteria were held at various temperatures (4 °C, 22 °C and 45 °C), acid concentrations (pH 3, 3.5 and 7) and salt concentrations (0%, 0.8%, 10% and 15% NaCl), and simultaneously exposed to 405 nm light. Enhanced inactivation of both E. coli and L. monocytogenes was achieved when light exposure was combined with each of the sub-lethal stresses, with significantly increased inactivation rates compared to non-stressed populations (P ≤ 0.05). One exception was with L. monocytogenes when light-exposed in the presence of 15% salt, as this combination reduced bacterial inactivation. The greatest enhancement of 405 nm light inactivation for both bacterial species was achieved when light exposure was combined with sub-lethal acid stress conditions at pH 3. This was demonstrated by a 5-log10 reduction of E. coli following a 405 nm light dose of 84 J/cm2 compared to 378 J/cm2 for non-stressed populations (77% reduction in dose) and by a 5-log10 reduction of L. monocytogenes achieved with a dose of 42 J/cm2 which corresponded to 50% of the dose required for the equivalent reduction of non-stressed populations. This acid-enhanced 405 nm light inactivation effect was demonstrated with E. coli and L. monocytogenes when dispersed in liquid suspension and when deposited on a test surface. Overall, results from this study have shown that sub-lethally stressed bacteria have increased susceptibility to 405 nm light inactivation, thereby providing a synergistic inactivation effect, findings which increase the potential of this new light-based decontamination technology for food related applications.
Original languageEnglish
Pages (from-to)91-98
Number of pages8
JournalInternational Journal of Food Microbiology
Volume170
Early online date2 Nov 2013
DOIs
Publication statusPublished - 17 Jan 2014

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Listeria
Listeria monocytogenes
Escherichia coli
inactivation
Salts
salts
Light
Temperature
Acids
acids
temperature
Bacteria
dosage
Dosimetry
Population
bacteria
Decontamination
Disinfection
Food Technology
decontamination

Keywords

  • 405 nm visible light
  • decontamination
  • food
  • bacteria
  • environmental stress

Cite this

@article{b205105d82cc49c2a5db44b4992e1469,
title = "Enhanced inactivation of Escherichia coli and Listeria monocytogenes by exposure to 405 nm light under sub-lethal temperature, salt and acid stress conditions",
abstract = "The antimicrobial effects of 405 nm light have generated interest in its use as an emerging disinfection technology with potential food-related applications. The aim of this study was to assess the bactericidal efficacy of 405 nm light for inactivation of Escherichia coli and Listeria monocytogenes under sub-lethally stressed environmental conditions. Bacteria were exposed to 405 nm light from a light emitting diode (LED) array under various temperature, salt (NaCl) and acid conditions to determine if bacterial susceptibility to 405 nm light inactivation is affected when exposed under these conditions. Non-stressed bacterial populations (105 CFU/mL) were exposed to increasing doses of 405 nm light (~ 70 mW/cm2) and the inactivation results were compared with those generated under stress conditions. Bacteria were held at various temperatures (4 °C, 22 °C and 45 °C), acid concentrations (pH 3, 3.5 and 7) and salt concentrations (0{\%}, 0.8{\%}, 10{\%} and 15{\%} NaCl), and simultaneously exposed to 405 nm light. Enhanced inactivation of both E. coli and L. monocytogenes was achieved when light exposure was combined with each of the sub-lethal stresses, with significantly increased inactivation rates compared to non-stressed populations (P ≤ 0.05). One exception was with L. monocytogenes when light-exposed in the presence of 15{\%} salt, as this combination reduced bacterial inactivation. The greatest enhancement of 405 nm light inactivation for both bacterial species was achieved when light exposure was combined with sub-lethal acid stress conditions at pH 3. This was demonstrated by a 5-log10 reduction of E. coli following a 405 nm light dose of 84 J/cm2 compared to 378 J/cm2 for non-stressed populations (77{\%} reduction in dose) and by a 5-log10 reduction of L. monocytogenes achieved with a dose of 42 J/cm2 which corresponded to 50{\%} of the dose required for the equivalent reduction of non-stressed populations. This acid-enhanced 405 nm light inactivation effect was demonstrated with E. coli and L. monocytogenes when dispersed in liquid suspension and when deposited on a test surface. Overall, results from this study have shown that sub-lethally stressed bacteria have increased susceptibility to 405 nm light inactivation, thereby providing a synergistic inactivation effect, findings which increase the potential of this new light-based decontamination technology for food related applications.",
keywords = "405 nm visible light, decontamination, food, bacteria, environmental stress",
author = "Karen McKenzie and Michelle MacLean and Igor Timoshkin and Scott MacGregor and John Anderson",
year = "2014",
month = "1",
day = "17",
doi = "10.1016/j.ijfoodmicro.2013.10.016",
language = "English",
volume = "170",
pages = "91--98",
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TY - JOUR

T1 - Enhanced inactivation of Escherichia coli and Listeria monocytogenes by exposure to 405 nm light under sub-lethal temperature, salt and acid stress conditions

AU - McKenzie, Karen

AU - MacLean, Michelle

AU - Timoshkin, Igor

AU - MacGregor, Scott

AU - Anderson, John

PY - 2014/1/17

Y1 - 2014/1/17

N2 - The antimicrobial effects of 405 nm light have generated interest in its use as an emerging disinfection technology with potential food-related applications. The aim of this study was to assess the bactericidal efficacy of 405 nm light for inactivation of Escherichia coli and Listeria monocytogenes under sub-lethally stressed environmental conditions. Bacteria were exposed to 405 nm light from a light emitting diode (LED) array under various temperature, salt (NaCl) and acid conditions to determine if bacterial susceptibility to 405 nm light inactivation is affected when exposed under these conditions. Non-stressed bacterial populations (105 CFU/mL) were exposed to increasing doses of 405 nm light (~ 70 mW/cm2) and the inactivation results were compared with those generated under stress conditions. Bacteria were held at various temperatures (4 °C, 22 °C and 45 °C), acid concentrations (pH 3, 3.5 and 7) and salt concentrations (0%, 0.8%, 10% and 15% NaCl), and simultaneously exposed to 405 nm light. Enhanced inactivation of both E. coli and L. monocytogenes was achieved when light exposure was combined with each of the sub-lethal stresses, with significantly increased inactivation rates compared to non-stressed populations (P ≤ 0.05). One exception was with L. monocytogenes when light-exposed in the presence of 15% salt, as this combination reduced bacterial inactivation. The greatest enhancement of 405 nm light inactivation for both bacterial species was achieved when light exposure was combined with sub-lethal acid stress conditions at pH 3. This was demonstrated by a 5-log10 reduction of E. coli following a 405 nm light dose of 84 J/cm2 compared to 378 J/cm2 for non-stressed populations (77% reduction in dose) and by a 5-log10 reduction of L. monocytogenes achieved with a dose of 42 J/cm2 which corresponded to 50% of the dose required for the equivalent reduction of non-stressed populations. This acid-enhanced 405 nm light inactivation effect was demonstrated with E. coli and L. monocytogenes when dispersed in liquid suspension and when deposited on a test surface. Overall, results from this study have shown that sub-lethally stressed bacteria have increased susceptibility to 405 nm light inactivation, thereby providing a synergistic inactivation effect, findings which increase the potential of this new light-based decontamination technology for food related applications.

AB - The antimicrobial effects of 405 nm light have generated interest in its use as an emerging disinfection technology with potential food-related applications. The aim of this study was to assess the bactericidal efficacy of 405 nm light for inactivation of Escherichia coli and Listeria monocytogenes under sub-lethally stressed environmental conditions. Bacteria were exposed to 405 nm light from a light emitting diode (LED) array under various temperature, salt (NaCl) and acid conditions to determine if bacterial susceptibility to 405 nm light inactivation is affected when exposed under these conditions. Non-stressed bacterial populations (105 CFU/mL) were exposed to increasing doses of 405 nm light (~ 70 mW/cm2) and the inactivation results were compared with those generated under stress conditions. Bacteria were held at various temperatures (4 °C, 22 °C and 45 °C), acid concentrations (pH 3, 3.5 and 7) and salt concentrations (0%, 0.8%, 10% and 15% NaCl), and simultaneously exposed to 405 nm light. Enhanced inactivation of both E. coli and L. monocytogenes was achieved when light exposure was combined with each of the sub-lethal stresses, with significantly increased inactivation rates compared to non-stressed populations (P ≤ 0.05). One exception was with L. monocytogenes when light-exposed in the presence of 15% salt, as this combination reduced bacterial inactivation. The greatest enhancement of 405 nm light inactivation for both bacterial species was achieved when light exposure was combined with sub-lethal acid stress conditions at pH 3. This was demonstrated by a 5-log10 reduction of E. coli following a 405 nm light dose of 84 J/cm2 compared to 378 J/cm2 for non-stressed populations (77% reduction in dose) and by a 5-log10 reduction of L. monocytogenes achieved with a dose of 42 J/cm2 which corresponded to 50% of the dose required for the equivalent reduction of non-stressed populations. This acid-enhanced 405 nm light inactivation effect was demonstrated with E. coli and L. monocytogenes when dispersed in liquid suspension and when deposited on a test surface. Overall, results from this study have shown that sub-lethally stressed bacteria have increased susceptibility to 405 nm light inactivation, thereby providing a synergistic inactivation effect, findings which increase the potential of this new light-based decontamination technology for food related applications.

KW - 405 nm visible light

KW - decontamination

KW - food

KW - bacteria

KW - environmental stress

UR - http://www.journals.elsevier.com/international-journal-of-food-microbiology

U2 - 10.1016/j.ijfoodmicro.2013.10.016

DO - 10.1016/j.ijfoodmicro.2013.10.016

M3 - Article

VL - 170

SP - 91

EP - 98

JO - International Journal of Food Microbiology

JF - International Journal of Food Microbiology

SN - 0168-1605

ER -